THE ELECTROCHEMICAL PROTON GRADIENT IN THE PHOTOSYNTHETIC PURPLE SULPHUR BACTERIUMCHROMATIUM VINOSUM

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Abstract
Cells of the photosynthetic purple bacteriumChromatium vinosumgenerate a transmembrane electrochemical proton gradient (δμH+H+) on illumination. The steady state values of the two components of δμH+m+, δpH and the membrane potential (δψ) have been measured as a function of both the pH and ion composition of the external medium. While δψ and δpH vary considerably as the external pH is varied from 5.5 to 7.5, the magnitude of δμH+h+remains relatively constant over this pH range. δψ is relatively unaffected by the ion composition of the medium but δpH and δμH+H+both vary considerably depending upon the cation present in the medium. The use of specific ionophores to eliminate either δpH or δψ results in changes in the magnitude of the other component. The δpH values determined here were used to predict the direction of Tl+flux via the potassium‐proton antiport and to demonstrate the reversibility of this antiport.